Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.52	5.504%	$134.5387	$134.54	$134.55	$134.50
Purchase #2	$20.61	8.239%	$22.3081	$22.31	$22.30	$22.30
Purchase #3	$168.29	4.199%	$175.3565	$175.36	$175.35	$175.40
Purchase #4	$147.66	3.298%	$152.5298	$152.53	$152.55	$152.50
Purchase #5	$247.86	9.274%	$270.8465	$270.85	$270.85	$270.80
Purchase #6	$19.89	4.105%	$20.7065	$20.71	$20.70	$20.70
Purchase #7	$59.47	11.227%	$66.1467	$66.15	$66.15	$66.10
7 purchase totals =	$791.30		$842.4328	$842.45	$842.45	$842.30